Generator protective device



2 Sheets-Sheet 1 Filed Dec. 19, 1951 INVENTOR. HAROLD S. GILLESP/E A? TOKNEY Sept. 14, 1954 H. s. GILLESPI GENERATOR PROTECTIVE DEVICE 2 Sheets-Sheet 2 Filed Dec. 19, 1 951 I INVENTOR. HAROLD s. G/L LESP/E Patented Sept. 14, 1954 UNITED STATES PATENT OFFICE GENERATOR PROTECTIVE DEVICE Harold S. Gillespie, Hasbrouck Heights, N. 3., assignor to Bendix Aviation Corporation, Teter- 'boro, N. J., a corporation of Delaware 1 Claim.

The present invention relates to protective systems for dynamoelectric machines and more particularly to protective systems for faults on generator feeders.

In airplanes, it is highly expedient to protect the electrical system against trouble of all kinds, not only to protect the electrical equipment but also to prevent any potential fire hazard from developing. Generators of the type used in airplanes normally are provided with overvoltage and overload protection. Due to the load on the generator, it is necessary that the overload protection be set high enough to carry normal loads. In order to protect for faults in the generator load line that may develop that would not be sufficient to operate the overload protective device, fault protection is incorporated in the protective device. Most generator control and protective systems for airplanes include some sort of field breaker which opens the generator field circuit at one or more points upon the occurrence of a ground fault. However, should a fault occur across the main output terminals or on the positive feeder, the generator will continue to feed the fault to maintain an are or produce high resistance heating at the point of the fault.

In the present invention means are provided to connect the shunt field in opposition to the series field upon the occurrence of a fault. Thus, the voltage drop in the series field due to the short circuit current would be impressed on the shunt field in such a direction as to cause a reverse current to flow in the shunt field which reduces the net M. M. F. producing flux across the air gap of the generator and reduces or kills the short circuit current of the generator.

It is an object of the present invention to provide improved fault protection for a dynamoelectric machine.

Another object of the invention is to provide an improved protective system for generators.

Another object of the invention is to provide means for reducing short circuit currents which persist after the main field has been opened.

These and other objects and features of the invention Will appear more fully hereinafter from a consideration of the following description taken in connection with the accompanying drawings wherein two embodiments of the invention are illustrated by way of example.

In the drawings:

Figure 1 is a schematic diagram of a generator and associated circuits embodying one form of the invention.

Figure 2 is a schematic diagram of a generator 2 and associated circuits embodying another form of the invention.

Referring now to Figure 1 of the drawing,

. there is provided a generator I having output lines 2 and 3, field winding 4 and interpole and compensating winding 5. The winding 5 is connected in series with one output terminal of the generator I and the output line 2. A ground connection 2A connects the line 2 to ground. The field winding 4 is connected at one end to the output line 2 by a conductor 6. The other end of the winding 4 is connected by a conductor I to a contact 8 which is controlled by a switch member 53. The switch member 9 cooperates with a second switch contact ll]. Leading from the switch contact I 0 is a conductor I l which in turn is connected to one end of a variable resistance carbon pile element I2. The other end of the carbon pile element I2 is connected by a conductor l3 to a switch contact I4 controlled by a switch member [5 which cooperates with a second switch contact l6. Leading from the switch contact I6 is a conductor I1 which is connected to the output line 3.

A winding I8 is connected by conductors I9 and 20 across the output of the generator I and provides electromagnet means which are so arranged in carbon pile regulator 21 as to control an armature 22 thereof and thereby the pressure applied to the carbon pile I2. The regulator 2| is shown diagrammatically in the drawing as including the armature 22 pivoted at 23 and exerting a compressive force upon the carbon pile [2 under the tension of a spring 24. The spring 2 3 is arrangedso as to balance the pull on the armature 22 by the electromagnet I8 when energized by a line voltage having a predetermined value. A variable resistance 25 inserted in the conductor 20 permits adjustment of the electromagnet la. The regulator 2| may be of a type such as shown in U. S. Patent No. 2,427,805, granted September 23, 1947 to William G. Neild.

Leading from the conductor I is a conductor 26 connected to one end of a potential coil 21. The other end of the coil 27 is connected by a conductor 28 to one end of a resistor 29. The other end of the resistor 29 is connected by a conductor 30 to the output line 2. With the switch members 9 and I5 in the closed position as shown, itwill be seen that the carbon pile I2 will 'be connected in series with the field 4 of the generator I so as to regulate the voltage across the lines 2 and 3.

Leading from the output line 3 is a conductor 3| connected to a switch contact 32 controlled by a switch member 33 which cooperates with a second switch contact 34. The switch contact 34 is connected by a conductor 35 to an electromagnetic winding 36. The winding 36 is grounded at the opposite end by a conductor 31. The winding 36 controls a main line circuit breaker 38 which is biased in a circuit open position by a spring 39.

The switch members 9, I and 33 are biased under tension of a spring 40 in a direction for opening the aforenoted respective circuits controlled thereby but are held from opening by a latch member 4| pivoted at 42 under tension of a spring 43 so as to lock the switch members 9, I5 and 33 in the closed position as shown. The switch members 9, I5 and 33 are mechanically connected by a suitable rod 44. Thus, the switch members 9, I5 and 33 are normally held in a circuit closing position by the latch member 4|. The latch member 4| is controlled by the winding 21 which is connected as previously described across the field winding 4 of the generator I.

The portion of the control system as set forth above is of the type such as is shown in Reissue Patent No 23,551 granted to William F. Fell and U. S. Patent No. 2,522,601 granted to Robert L. Brown.

The fault detecting portion of the control circuit may be of the type disclosed and claimed in application serial No. 135,681, filed December 29, 1949 by William R. Holmes, however, it is understood that other methods of fault detecting may be used.

In order to detect faults, a sensitive differential type relay 46 is provided and comprises a movable armature 41, contacts 48 and 49 and coils 50 and 5|. The coil 50 is connected by conductors 52 and 53 across a resistance 54 located in the line 3 while one end of the coil 5| is connected by conductor 55 to a movable tap 56 on a potentiometer 51. The potentiometer 51 is connected across the interpole and compensating winding 5. The other end of the coil 5| is connected by conductor 58 to the output line 2. The contacts 48 and 49 are connected by a conductor 59 to the conductor 28 and the armature 41 is connected by a conductor 60 to the output line 2.

A novel feature of the present invention is providing contacts BI and 62 to cooperate with the switch member 9 when in an open circuit position. The contact 6| is connected by a conductor 63 to the contact 8. The contact 62 is connected by a resistor 64 and conductor 65 to the negative output of the generator I.

In operation, the potentiometer 5! is adjusted so that under normal load conditions, the voltage drop across the potentiometer 51 and resistor 54 are equal hence the flow of current in the coils 50 and 5| will be equal. Inasmuch as they are opposing, the effect of each on the armature 41 will be canceled permitting it to remain in a neutral position.

Upon the occurrence of a fault between the positive feeder and ground (or between the positive and negative feeders in an ungrounded system) the voltage drop across the resistor 54 and potentiometer 51 will be of unequal value due to the difference in current flowing in the output lines 2 and 3. This difference in voltage drop will cause one of the coils 50 or 5| of the relay 46 to exert a greater pull on the armature 47 thus moving it from the neutral position into operative relationship with one of the contacts depending upon the direction of unbalance.

Upon the armature 4l being actuated to engage either contact, the resistance 29 is short circuited. This increases the voltage applied to the coil 21 to a value above the predetermined minimum necessary to apply sufiicient pull on the latch member 4| to overcome the bias of the spring 43 and actuate the member 4| to permit the spring 40 to actuate the switch members 9, I5 and 33 to open the generator field circuit and also deenergize the circuit for controlling the main line switch 38 thereby isolating the fault.

The switch member 9 upon actuation to the open circuit position coacts with the contacts 6| and 62 to connect the field winding 4 in opposition to the series winding 5. The voltage drop in the series winding 5 due to any short circuit current will be impressed on the field winding 4 in such a direction as to cause a reverse current to flow in field 4 which will in turn reduce the net M. M. F. producing flux across the air gap of the generator I and reduce or kill the short circuit current being put out by the generator. The resistor 64 limits the reverse current in the field 4 to a value which will not reverse the residual magnetism of the field circuit but will reduce the short circuit output to a point where it will fall ofi and will not build up again.

Referring now to Figure 2, wherein another embodiment of the invention is illustrated, there is provided a generator 15 having output lines I6 and 11, a field winding I8 and interpole and compensating winding I9. The winding I9 is connected in series with one output terminal of the generator 15 and the output line I6. A ground connection connects the line I6 to ground. The field winding 18 is connected at one end to the line I6 by a conductor 8|. The other end of the winding I8 is connected by a conductor 82, switch 83 and conductor 84 to one side of a carbon pile resistance element 85 of a regulator 86. The other end of the carbon pile element 85 is connected by conductor 81, switch 88 and conductor 89 to the output line 11.

The regulator 86 is shown diagrammatically as including an armature 90 pivoted at 9| and exerting a compressive force upon the carbon pile 85 under the tension of a spring 92. The spring 92 is arranged so as to balance the pull on the armature 90 by electromagnetic windings 93 and 94. One end of the winding 93 is connected by conductor 95 to ground. The other end of the winding 93 is connected by conductor 96, switch 91 and conductor 98 to the output line I1. A variable resistor 99 may be inserted in the conductor 96 to permit adjustment of the winding 93.

One end of the winding 94 is connected by conductor I00 to fixed contacts I6! of parallel relay I02. Movable contacts I03 of the relay I02 are connected by a conductor I04 to equalizer bus I05. The other end of the winding 04 is connected by conductor I06 to movable contact I07 of a resistor I08. One end of the resistor I08 is connected by a conductor I09 to ground. The other end of the resistor I08 is connected by a conductor III! to the D terminal or negative brush of the generator I5.

The relay I02 has an electromagnetic winding III one end of which is connected by conductor II 2, resistor II3, conductor I I4, switch H5 and conductor II6 to ground. The other end of the winding III is connected by a conductor III to the conductor 96.

A switch arm I I8 of pilot relay H9 is also connected to the conductor H1. The switch arm III! in its normally open position cooperates with a contact I connected to conductor H2 and provides a shunt across the winding III. The :pilot relay I I3 has an electromagnet winding 121, one end of which is connected to the conductor Ill. The other end is connected by a resistor I22 to the conductor IM. Thus, the winding I2! is connected across the output of the generator It by conductors 98, switch 31, conductor 96., conductor II'I, resistor I22, conductor I It, switch I I5 and conductor H6. The switch member I I 8 when actuated to a closedposition cooperates with contact l23of the relay H9. The-contact I23 isconnected by a conductor I24 to one end of electromagnet winding I25 of a polarized differential voltage reverse current relay I26. The contact -I 23 is also connected by a resistor I27 to the conductor Ill.

The other end of the winding I25 connected by conductor I 28, switch member I23 and conductor I30 to the output line TI, The winding I25 actuates a switch member I3! in a dire Ion dependent upon the direction of current flowing through the winding I25. One side of the switch member is connected by a conductor I32 to the conductor 8?. When. in a closed position, the switch member cooperates with a Contact I33 which is connected by conductor I34, switch. and conductor I36 to one end of electromagnet winding I3! of contactor I38. The other end of the winding I37 is connected to grounded conductor I39. Therelay I26 also has a reverse current winding I40, one end of which is connected by a conductor I II to ground. The other end of the winding Iii] is connected by a conductor I42 to the conductor III].

Overvoltage and ground fault detecting panel I33 is comprised generally of a locating relay WI, an overvoltage relay I45 and a ground fault relay I48.

The locating relay I44 has an eleotromagnet winding I I! one end of which is connected by conductor I48 to the conductor I33. The other, end of the winding I I? is connected by a corn ductor I49 to ground. Switch member I33 of the relay I44 is connected by a conductor I5! to the movable tap It! of the resistor I33. When actu ated to the closed position by energization of the winding I I'I, the switch member Ififl cooperates with contact I52 connected by conductor I 53 to one end of locating winding I54- of the overvoltage relay I35. The other end of the winding IE4 is connected by conductor I55 to locating bus I56.

In addition to the locating winding I54, the overvoltage relay has a winding I51, one end of which is connected by conductor I53 to the conductor I49. The other end of the winding I5; is connected by a temperature compensating network !59 and conductor I60 to the conductor Ill. The windings I54 and I 5? coact to actuate switch members ItI. The switch members IEI are connected by a conductor I32 to one side of a trip winding I33 on main circuit breaker I34. A resistor I may be inserted in the conductor I62. The other end of the winding IE3 is connected by a conductor I65 to the conductor 81. The switch member I6! coacts when in the closed position with contacts Ifil. The contacts I81 are con-- nected by a conductor I58 to the conductor I III.

The main circuit breaker IE4 may be of the type described and claimed in U. S. Patent No. 2,560,628, issued July 17. 1953. to Robert L. Brown, and controls a switch member I39 in the output line TI, also switch members 83, I28, 3'! and I23. In addition to the trip winding I63, the breaker I64 i of the generator I5.

has a current winding il'lii in series in the output line H, a balancing winding Ill and areset winding I'l'2. The'reset winding 17?: has oneend connected by conductor I13 and switch I14 to main bus I15. The other end of the winding I I2 is connected to ground. In addition, the breaker I34 a manual reset I76. One end of the balancing winding I'll is connected by a conductor Ii"! to the conductor I II The other end of the winding El! is connected by a conductor I1 8 to the grcundedconnection I49. A blocking rectifier I755 may be inserted in the conductor I78 to provide reverse current protection.

A novel feature of the invention resides in the means for protection against faults such as, for example, grounds. The ground fault relay I43 may be of a sensitive differential type and has a movable armature I80,contacts I8! and I82, and coils I83 and I34. The coil I33 is connected by conductors I85 and I33 across a resistance I3? located in the output line H. The coil I34 is con nected by conductors I88 and I89 across a resistance I93 located in the line '16. The contacts NH and I32 are interconnected by conductor IEI and connected to the contacts I37 of the relay I45. The armature I8!) is connected by a conductor I32 to one end of electromagnet winding I93. The other end of the winding I33 is connected by conductor I94 to the conductor 3?.

The winding I93, when energized, actuates switch member I35 from a normally open position into cooperation with contact I96. The switch member I95 may be biased in the open position by a spring I97 or in any other conventional man ner such as are well known in the art. The switch I33 is retained in the closed position by a latch member I33. It is understood, however, that other means may be used for retaining the switch member in the closed position.

The switch member I95 is connected by a conductor I99 to the conductor 32. The contact I98 is connected by conductor 233 to the conductor III). A resistor 26H may be inserted in the corn ductor 208 to prevent a reversal of the polarity The conductor I32 is connected by a conductor 202 to the conductor I32. A blocking rectifier 233 may be inserted in the conductor 232 to prevent energization of the winding I93 upon the over-voltage relay I45 only closing.

In operation, with the main breaker I54 and switches H5 and I35 in the closed position, the winding I2! is connected across the generator output and is so proportioned to overcome the bias of switch arm I Is to actuate it into contact with contact I23 upon the voltage of the generator rising to a predetermined value. Actuation of the switch arm H8 removes the short circuit from the winding III which actuates the switch members I03 to a closed position to connect the equalizer winding 94 to the system. The winding 94 affects the regulator 86 in a directionto raise the generator voltage slightly above the bus voltage. Upon the generator exceeding the bus voltage by a predetermined amount, the differential and reverse current relay I26 energizes the contactor coil I31 which actuates contactor I38 to connect the generator to the bus.

The current winding I40 of relay I26 is poled to normally hold the switch member in a closed position, however upon reverse current flowing in the generator, it actuates the member I3] to an open-circuit position thereby deenergizing the coil I31 to open the contactor I 38.

Upon an overvoltage occurring, the overvoltage relay I45 energizes the trip coil I83 to open the breaker I64. The locator winding I54 coacts with the winding I51 to sense the overvoltage and also prevents the unafiected generators from being removed from the bus. The locating relay I44 connects the winding I54 in the system as the generator is connected to the bus. The blocking rectifier 203 prevents the Winding I93 from being energized on an overvoltage.

Fault protection is obtained from the ground fault relay I46 operable upon an unbalance of current flowing from the generator. While shunts have been illustrated to detect the unbalance, it is understood that other methods may be used. Upon an unbalance occurring in either direction, the armature I80 is actuated into cooperation with one or the other of contacts I8I and I82. This completes a circuit through the rectifier 203 to energize the trip winding I63. to actuate the switch member I95 to a closed position to connect the positive field lead through a limiting resistor to the negative brush of the generator. Thus, the voltage drop in the series field due to the fault would be impressed on the shunt field in such a direction to cause a reverse current to fiow therein and reduce the net M. M. F. producing flux across the air gap of the generator. The latch member I98 retains the switch member I95 is a closed position so that it will not open up upon the coil I93 being deenergized by the opening of the main breaker and associated switches.

Although only two embodiments of the invention have been illustrated and described, various changes in the form and relative arrangement of the parts may be made to suit requirements.

What is claimed is:

A protective system for a generator supplying a load bus through output conductors and having a main field winding and a series field winding, comprising a voltage regulator for controlling the The winding I93 is also energized 1 excitation of the main field winding to maintain a predetermined output voltage, first switch means for connecting said generator to said load bus, first relay means for causing said first switch means to disconnect said generator from said load bus, second switch means for controlling the energization of said main field winding, second relay means for causing said second switch means to deenergize said main field winding, said second switch means being normally closed to complete the main field circuit, an overvoltage relay operable upon said generator voltage exceeding a predetermined maximum to energize said first relay means to cause said first switch means to open said connection between said generator and load bus, a fault relay operable in response to the occurrence of a fault in said generator or its output conductors to cause said first and second relay means to open said first and second switch means, and other circuit means to connect said main field winding in opposition to said series field Winding, third switch means to control said other circuit means, means operably connecting said second relay means to said third switch means to render said other circuit means effective in response to the operation of said fault relay, blocking means between said overvoltage relay and said fault relay to prevent operation of said second relay means upon operation of said overvoltage relay.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,534,895 Austin et a1. Dec. 19, 1950 FOREIGN PATENTS Number Country Date 129,068 Great Britain July 2, 1919 156,868 Great Britain Jan. 20, 1921 

